1. Field of the Invention
The invention relates to a method for controlling a stepping motor whose field windings are connected to a switching device which sets the magnitude and direction of the phase currents in the field windings as a function of the vector angle of a required vector which is switched onwards by one step angle per interval of a system clock, which step angle is dependent on stored values which are read out in the direction of increasing values for acceleration and in the reverse direction for braking.
2. Description of the Related Art
Such a method is known from U.S. Pat. No. 4,280,084. There, the current step angle is formed as the sum of a constant coarse step and a fine step whose value rises or falls from step to step and is read from a memory. In this way, the lag angle (angular difference between the field vector and the rotor position) and thus the torque are held at their initial maximum value despite the changing rotor speed.
The invention is based on the knowledge that, during acceleration/deceleration with the maximum moment at the start and end of a displacement, the shortest possible displacement time is never achieved and that the suddenly acting high moment excites the stepping motor to oscillate, which frequently leads to step losses. Finally, this also results in an unfavorable dimensioning of the stepping motor since its maximum moment is utilized only briefly.